Backward Adaptive Brightness Temperature Threshold Technique (BAB3T): A Methodology to Determine Extreme Convective Initiation Regions Using Satellite Infrared Imagery

Maite Cancelada,Stephen W Nesbitt,Daniel Vila,Paola Salio,Luciano Vidal

doi:10.3390/rs12020337

Abstract

Thunderstorms in southeastern South America (SESA) stand out in satellite observations as being among the strongest on Earth in terms of satellite-based convective proxies, such as lightning flash rate per storm, the prevalence for extremely tall, wide convective cores and broad stratiform regions. Accurately quantifying when and where strong convection is initiated presents great interest in operational forecasting and convective system process studies due to the relationship between convective storms and severe weather phenomena. This paper generates a novel methodology to determine convective initiation (CI) signatures associated with extreme convective systems, including extreme events. Based on the well-established area-overlapping technique, an adaptive brightness temperature threshold for identification and backward tracking with infrared data is introduced in order to better identify areas of deep convection associated with and embedded within larger cloud clusters. This is particularly important over SESA because ground-based weather radar observations are currently limited to particular areas. Extreme rain precipitation features (ERPFs) from Tropical Rainfall Measurement Mission are examined to quantify the full satellite-observed life cycle of extreme convective events, although this technique allows examination of other intense convection proxies such as the identification of overshooting tops. CI annual and diurnal cycles are analyzed and distinctive behaviors are observed for different regions over SESA. It is found that near principal mountain barriers, a bimodal diurnal CI distribution is observed denoting the existence of multiple CI triggers, while convective initiation over flat terrain has a maximum frequency in the afternoon.

Highlights

The occurrence of severe deep moist convection over southeastern South America (SESA; area enclosed by solid black box in Figure 1) produces high impact weather events that directly impact the population, water resource management and agricultural production in the region [1,2,3,4,5,6].Studies using data from multiple satellite platforms have shown that deep extreme and horizontal organized convection occurs in continental subtropical South America [7,8,9,10,11,12]
These studies show that deep moist convection, mesoscale convective systems (MCSs), reach extreme characteristics of size and duration, and dominate rainfall production compared with other regions of the world [13,14]
The determination of convective initiation (CI) location using BAB3T is evaluated over three different Extreme rain precipitation features (ERPFs) backward tracked cases over SESA: 20 October 2012, 28

Summary

Introduction

The occurrence of severe deep moist convection over southeastern South America (SESA; area enclosed by solid black box in Figure 1) produces high impact weather events (e.g., hail, tornadoes, flooding, damaging winds) that directly impact the population, water resource management and agricultural production in the region [1,2,3,4,5,6].Studies using data from multiple satellite platforms have shown that deep extreme and horizontal organized convection occurs in continental subtropical South America [7,8,9,10,11,12]. In the absence of a monitoring ground-based weather radar network, earlier studies such as the pioneering work of Velasco and Fritsch [15] were mainly conducted using thermal infrared channels from geostationary satellite platforms Other authors such as Machado et al [16], Nieto Ferreira et al [17], Siqueira et al [18], Salio et al [19], Anabor et al [20], Vila et al [21], Durkee and Mote [22], among others have explored more complete characterization of these MCSs lifecycles (i.e., spatial and temporal distribution, directions of travel, maximum sizes attained, among others). A combination of infrared sensors on geostationary platforms and TRMM-GPM radar information are ideal to understand the evolution of convective systems and determine initiation regions (e.g., [28]) over regions without the presence of long records of ground weather radar networks

Objectives

Results

Discussion

Conclusion